Featured Project

OPEX - Multi-Platform Expense Management System

Real-time expense tracking and task management system for field workers and administrative teams

8-10 months development cycle

3 developers (backend, frontend, mobile specialists)

Featured

Project Overview

OPEX is a comprehensive expense management platform designed for field service companies, featuring real-time task synchronization across web and mobile devices. It enables field workers to capture receipts, track time, and manage tasks while providing administrators with powerful oversight and reporting capabilities. The system supports multi-tenant architecture with role-based permissions and automated task generation using AI.

The Problem

Field service companies struggle with fragmented expense tracking, inefficient paper-based receipt management, and lack of real-time coordination between field workers and office staff, leading to delayed reimbursements and poor visibility into operational costs.

The Solution

OPEX provides a unified platform with mobile apps for field workers to instantly capture receipts and log expenses, while offering a web dashboard for administrators to manage, approve, and analyze expenses in real-time. The solution uses AI-powered receipt processing, real-time SSE synchronization for cross-device focus mode, and integrates with existing accounting systems.

Key Features

Real-Time Cross-Platform Focus Mode: Synchronizes task focus across all devices instantly using Server-Sent Events, allowing teams to coordinate work in real-time

AI-Powered Receipt Processing: Automatically extracts data from receipt photos using LLM integration (Claude/Gemini) for instant expense categorization

Multi-Tenant Architecture: Supports multiple companies with isolated data, custom branding, and role-based permissions for employees, managers, and administrators

Offline-First Mobile Experience: React Native app with camera integration for receipt capture, works offline and syncs when connection is restored

Comprehensive Time & Task Management: Track time entries, manage task assignments, set deadlines, and organize work with custom views and tags

Automated Reporting & Integration: Generate expense reports, integrate with accounting systems, and automate task creation based on patterns

Challenges

Real-Time Synchronization Complexity: Implementing reliable cross-platform real-time updates between web and mobile clients with different authentication methods (cookies vs JWT tokens) while handling network interruptions and automatic reconnection

Multi-Platform State Management: Maintaining consistent state across three different platforms (NestJS backend, React web, React Native mobile) with different state management solutions (Redux Toolkit vs Zustand)

Offline-First Architecture: Designing a mobile experience that works seamlessly offline for field workers in areas with poor connectivity, requiring local storage with MMKV and intelligent sync mechanisms

LLM Integration for Receipt Processing: Integrating multiple AI providers (Anthropic Claude and Google Gemini) for automated receipt data extraction while handling varying image quality and formats

Multi-Tenant Security: Ensuring complete data isolation between customers while maintaining efficient database queries and preventing cross-tenant data leaks in a shared PostgreSQL instance

Performance at Scale: Optimizing database queries with materialized views and proper indexing to handle thousands of concurrent users and millions of receipts/tasks

Results

Achieved 90% reduction in expense processing time through automated receipt capture and AI-powered data extraction

Successfully deployed real-time synchronization supporting 100+ concurrent field workers with sub-second latency

Reduced manual data entry errors by 85% through mobile-first design and automated validation

Enabled instant expense visibility for managers, cutting reimbursement cycles from weeks to days

Scaled to support multiple enterprise customers with 500+ users per tenant without performance degradation

Maintained 99.9% uptime on Google Cloud Platform with automatic failover and load balancing

Project Info

Timeline

8-10 months development cycle

Team Size

3 developers (backend, frontend, mobile specialists)

My Role

Full-Stack Development Team

Technologies

NestJSPostgreSQLTypeORMReactRedux ToolkitTanStack RouterReact NativeExpoServer-Sent Events (SSE)Google Cloud Platform (Cloud Run, Cloud SQL, Cloud Storage)JWT AuthenticationRadix UITailwind CSSNativeWindZustandReact Hook FormZodAnthropic Claude AIGoogle Gemini AIFirebase Cloud Messaging